In mammography systems, a compression device, such as a compression paddle, is used to compress the breast of a patient. Firm compression of the breast is essential for good quality mammography. Firm compression spreads out the breast structures, thereby reducing superimposed structures. Current breast compression devices compress the breast with the compression paddle being parallel to the image detector. For the craniocaudal view, these devices often provide good compression of the breast near the chest wall but inadequate compression toward the nipple. For the mediolateral view, current breast compression devices may not provide good compression for both the axilla and inferior or main breast. Such parallel compression devices provide roughly uniform tissue thickness. However, the breast is compressed with more force where the breast is thicker and less force where the breast is thinner. Therefore, in areas where the breast is thinner and compressed with less force, the image quality will be poor. A conventional mammography system is disclosed in U.S. Pat. No. 5,305,365 to Coe. This patent is hereby incorporated by reference.
FIG. 1 illustrates the regions of the breast as viewed from the superior or cranial side. The axillary tail 1 is located towards the armpit or axilla. The posterior 2, middle 3, anterior 4 and subareolar 5 make up the main lobe of the breast.
There are two standard views of the breast taken for a mammogram. FIG. 2a illustrates the mediolateral oblique view of the breast. The direction of the x-ray beam is indicated by arrow 6a. The image detector 7 extends from the axilla portion 8 of the breast to the inferior portion 9 or main lobe of the breast. The x-ray beam first enters the breast through the medial side 10 and exits through the lateral side 11. FIG. 2b illustrates the craniocaudal view of the breast. The direction of the x-ray beam is indicated by arrow 6b. The image detector 7 is placed under the main lobe 9 of the breast. The x-ray beam 6b enters the breast through the cranial or superior portion 12 of the breast and exits through the caudal or inferior portion 13 of the breast. For both of the two standard views, conventional systems do not generate enough compression of the entire breast tissue to provide good quality images for cancer detection. Therefore, using the conventional systems may result in inaccurate diagnoses.
A known compression paddle system which comes down at an angle was produced by Planmed of Helsinki, Finland. Planmed's mammography systems are motorized and can be controlled by foot pedals or switches. This conventional system is a two phase system. The first phase is the compression phase with steady compression. When a preset compression force is reached, an audible signal is given and the second phase of fine tuned compression can be applied. The breast is prepositioned by the technologist. During the first phase of compression, the chest wall side of the upper paddle is angled toward the image detector at the start of compression. As it descends and starts to compress the breast, the paddle begins to level and exert a two-phase force on the breast. At completion of the compression, the paddle is level or parallel to the image detector.